The present disclosure relates to a document conveying device that is mounted in an image forming apparatus such as a digital copy machine, a laser printer, or the like and feeds a document sheet one by one separately from a stack of document sheets, and to an image forming apparatus including the same.
Conventional image reading devices that are mounted in copy machines and so on utilizing the electrophotographic process may include a document conveying device (automatic document feeder) that sequentially feeds a document in sheet form onto a document placing table in order for it to be read and removes it from the document placing table after it has been read. An image reading device of this type is capable of performing the following two reading methods. One is a sheet-through method in which, with a document presser closed, a document sheet is read while being automatically conveyed by a document conveying device, and the other is a document stationary method in which, upon every completion of reading, the document presser is opened and closed in order for a document sheet on the document placing table (contact glass) to be replaced one by one.
In the former, namely, the sheet-through method, a document reading operation is performed with an optical system in the image reading device held at a predetermined image reading position without performing a scanning movement, whereas in the latter, namely, the document stationary method, a reading operation is performed while the optical system performs a scanning movement. In reading a document sheet based on the sheet-through method, generally, a pickup roller supported in a feeding unit is brought in press-contact with an uppermost surface of a stack of document sheets stacked on a document stacking tray, and the document sheet is conveyed in that state.
Typically, when a stack of document sheets are placed on the document stacking tray, by a manual operation, tip ends of the stack of document sheets in a feeding direction are made to butt against a predetermined butting member (stopper) provided in the feeding unit, and the tip ends of the stack of document sheets are thereby aligned with each other. The stopper is configured to be changeable between an opposedly fixed state where it is fixed so as to be opposed to a stack of document sheets on the document stacking tray and a fixing released state where it is swung so that the opposedly fixed state is released to allow passage of document sheets therethrough. For aligning tip ends of a stack of document sheets on the document stacking tray with each other, the stopper is set to be in the opposedly fixed state, while for feeding a document sheet one by one from the stack of document sheets by driving the feeding unit including the pickup roller and a feeding roller, the stopper is set to be in the fixing released state.
By the way, when, in setting a stack of document sheets on the document stacking tray, a user align send portions of the stack of document sheets with each other by use of the stopper, vibrations might occur to cause the feeding unit disposed at a standby position to be displaced downward, which has been problematic.
In order to prevent this trouble, there is known an automatic paper sheet feeding device that includes a stopper having a stopper piece that, from a support shaft supported in a support body (feeding unit) in which a pickup roller is supported, extends downward to become opposed to tip ends of paper sheets on a feeding tray and an engagement piece that is provided to protrude upward from the support shaft, and in which a restriction surface that restricts swinging of the stopper, which has been set to be in the opposedly fixed state, by being engaged with the engagement piece is provided on a main body side of the device.
In the above-described configuration, the engagement piece of the stopper and the restriction surface provided on the main body side of the device interfere with each other and thus can prevent the stopper from being brought into the fixing released state. With this configuration, however, for example, in a case where various parts of the document conveying device are driven by use of one motor, members to be driven including the feeding unit are each connected to the motor via a clutch.
In such a case, since the feeding unit is not always connected to be driven, there has been the following problem. That is, when, in setting a stack of document sheets, a user forcibly pushes in the stack of document sheets toward the stopper, a load in a document feeding direction is applied to the stopper, so that a force in a downward direction is exerted on the feeding unit in which the stopper is supported. As a result, the feeding unit might be displaced downward below a standby position thereof, causing the stopper, which has been set to be in the opposedly fixed state, to be brought into the fixing released state. Because of this, tip ends of the stack of document sheets accidentally reach as far as the vicinity of a nip portion (document separation portion) of a feeding roller pair, leading to the occurrence of double feeding or skew feeding of document sheets.